Hydroxyurea

What Is Hydroxyurea?

Hydroxyurea is a prescription medicine that belongs to a drug class called antimetabolites. It works by blocking an enzyme (ribonucleotide reductase) that cells need to make DNA. It is also called an antineoplastic (anti-cancer) medicine. It is taken by mouth. Hydroxyurea is sold under brand names such as Hydrea, Droxia, and Siklos, and generic versions are also available.

Approved Uses

In the United States, hydroxyurea products are FDA-approved for the following. The approved use depends on the specific product.

• Sickle cell anemia: to reduce how often painful crises happen and how often blood transfusions are needed, in people with recurrent moderate to severe painful crises. Some products are approved for adults only, and some are approved for children 2 years and older.
• Chronic myeloid leukemia (CML): in people whose disease has become resistant to other treatment
• Head and neck cancer: certain squamous cell cancers of the head and neck (not the lip), used together with radiation therapy

Other Prescribed Uses

Specialists sometimes prescribe hydroxyurea for other conditions that are not listed on the FDA label, such as certain bone marrow disorders that cause too many blood cells (for example, polycythemia vera or essential thrombocythemia). These decisions are individual and are made by an experienced specialist. This guide does not recommend use for any condition that is not FDA-approved.

Available Formulations and Strengths

• Capsules: Hydroxyurea 500mg (strengths vary by product)
• Tablets: 100 mg and 1,000 mg, for some products
• Oral liquid: available for some products in some regions

Products are not always interchangeable. Do not switch brands, strengths, or forms unless your specialist or pharmacist tells you to.

What Is the Recommended Dosage of Hydroxyurea?

There is no single dose that fits everyone. Your specialist decides the dose based on:

• The condition being treated
• Body weight, which is commonly used for dosing, especially in children
• Blood counts, which are checked often and guide dose changes
• Kidney function: people with reduced kidney function often need a lower dose
• Age and overall health
• Other medicines and treatments, including radiation

Available Dosage Forms

Hydroxyurea is usually taken by mouth once a day. In sickle cell anemia, treatment often starts at a lower dose and is slowly raised, based on blood tests, to the highest dose the person tolerates well. This is called dose escalation.

Follow Your Specialist’s Instructions

Doses may be raised, lowered, or paused depending on lab results and side effects. Take hydroxyurea exactly as prescribed. Do not change the dose or stop the medicine on your own. Drink plenty of fluids while taking it, unless told otherwise. If someone has trouble swallowing capsules or tablets, ask the pharmacist about approved ways to give the medicine and how to handle it safely. Do not crush or open capsules unless you have been given specific instructions.

How Hydroxyurea Works

Cells need to copy their DNA in order to divide. Hydroxyurea slows this process by blocking an enzyme that makes the building blocks of DNA.

• In cancer, slowing DNA production helps slow the growth of fast-dividing cancer cells. It is often part of a larger treatment plan.
• In sickle cell anemia, hydroxyurea raises the amount of fetal hemoglobin (a type of hemoglobin the body makes before birth) in red blood cells. Fetal hemoglobin helps keep red blood cells from becoming sickle-shaped and sticking together, which can lower the risk of painful crises. It also lowers certain white blood cells that can contribute to blocked blood vessels.

Hydroxyurea helps manage these conditions. It does not cure sickle cell anemia or leukemia. It can take weeks to months to see the full benefit, especially in sickle cell anemia.

Is a Prescription Required to Buy Hydroxyurea Online?

Yes. Hydroxyurea is a prescription-only medicine. It should be started and monitored by a licensed medical specialist, such as:

• A hematologist (blood specialist), for sickle cell anemia and blood cancers
• An oncologist, for leukemia and head and neck cancers

Buying Medicine Safely

• Use only licensed pharmacies that require a valid prescription.
• Be cautious of websites that sell hydroxyurea without a prescription. Products from these sources may be counterfeit, expired, contaminated, or the wrong strength.
• Do not use veterinary products or products from unverified sellers.
• If you are unsure whether a pharmacy is legitimate, ask your specialist, your local pharmacist, or your country’s pharmacy regulator.

Side Effects of Hydroxyurea

Not everyone has side effects. Regular blood tests help your care team catch problems early. Tell them about any new symptoms.

Common Side Effects

• Low blood cell counts (often found on blood tests)
• Nausea, vomiting, or upset stomach
• Diarrhea or constipation
• Loss of appetite
• Mouth sores
• Headache or dizziness
• Tiredness or drowsiness
• Hair thinning
• Skin rash, dryness, or darkening of the skin or nails
• Larger red blood cells (seen on blood tests, not usually harmful)

Serious Side Effects

• Severe drops in blood cell counts (bone marrow suppression): This can cause serious infections, bleeding, or severe tiredness and paleness.
• Increased risk of cancers: Long-term use has been linked to skin cancer and to leukemia.
• Skin problems: Painful leg ulcers or sores, and, in some people, skin changes on the hands and feet, have been reported.
• Kidney or liver problems
• Pancreatitis and liver injury, especially when taken with certain HIV medicines
• Lung problems
• Severe allergic reaction
• Lower sperm counts or fertility problems in males
• Harm to an unborn baby

When to Get Medical Help Right Away

Contact your specialist or seek emergency care if you have:

• Fever, chills, or signs of infection
• Unusual bleeding, bruising, or black stools
• Severe stomach or back pain
• Yellow skin or eyes, or dark urine
• Painful skin ulcers, especially on the legs or ankles
• Swelling of the face, lips, or throat, or trouble breathing
• A new or changing skin spot or growth
• A positive pregnancy test or possible pregnancy

Drug Interactions

Hydroxyurea can interact with other medicines and treatments.

Major Interaction Categories

• HIV medicines such as didanosine and stavudine: Taking these with hydroxyurea can lead to serious and sometimes fatal pancreatitis, liver problems, and nerve damage.
• Other medicines and treatments that lower blood counts: This includes chemotherapy and radiation, which may increase the risk of severe blood count drops.
• Interferon: Combined use may raise the risk of skin and blood vessel problems.
• Live vaccines: These are generally avoided during treatment because the immune system may be weakened. Ask your specialist before any vaccination.
• Other medicines that affect the kidneys, liver, or bone marrow: These may need extra monitoring.

Over-the-Counter Medicines

Ask a pharmacist or specialist before using OTC products, including pain relievers such as aspirin and ibuprofen, which can raise bleeding risk if blood counts are low.

Supplements and Herbal Products

Vitamins, supplements, and herbal products may interact with hydroxyurea or affect the liver or bone marrow. Do not start them without checking first.

Share a Full Medication List

Give your licensed medical specialist a complete list of everything you take, including prescription medicines, OTC medicines, supplements, and herbal products. Update the list whenever anything changes.

Safety & Important Considerations

Boxed Warnings from the FDA

The labeling for some hydroxyurea products includes boxed warnings, the FDA’s most serious type of warning, about bone marrow suppression and the risk of cancers (including leukemia and skin cancer). Read the Medication Guide that comes with your prescription.

Liver and Kidney Precautions

The kidneys help clear hydroxyurea from the body, so people with kidney problems often need lower doses. People with liver problems may also need closer monitoring.

Pregnancy, Fertility, and Breastfeeding

• Hydroxyurea can harm an unborn baby. Females who can become pregnant should have a pregnancy test before starting and use effective birth control during treatment and for a period afterward. Males with partners who can become pregnant should also use effective birth control during and after treatment. Your specialist will give the exact timing.
• Hydroxyurea can lower sperm counts. Males may want to discuss fertility options, such as sperm storage, before treatment.
• Breastfeeding is generally not advised during treatment and for a period afterward. Discuss with your specialist.
• Tell your specialist right away if you are pregnant, planning pregnancy, or become pregnant.

Children and Older Adults

• Children: Some products are approved for use in children with sickle cell anemia (2 years and older). Doses are usually based on weight, and growth and development are followed.
• Older adults: They may be more sensitive to side effects, and they are more likely to have reduced kidney function, so closer monitoring may be needed.

Monitoring

Expect regular blood tests, such as complete blood counts, and tests of kidney and liver function. Blood tests are often done every couple of weeks while the dose is being adjusted, and then less often once the dose is stable. Do not skip these visits.

Sun and Skin Protection

Hydroxyurea may increase skin cancer risk. Use sunscreen, wear protective clothing, and avoid tanning beds. Have skin checks as advised.

Safe Handling

Hydroxyurea is a hazardous drug. Caregivers should wash their hands before and after handling it and, if the medicine is handled in ways that could touch the skin (such as with broken capsules or crushed tablets), wear disposable gloves. Pregnant caregivers should ask a pharmacist about safe handling. If a capsule breaks or powder spills, ask your pharmacist how to clean it up safely. Do not touch spilled powder or liquid with bare hands.

Who This Medication Is For

Hydroxyurea is prescribed for people who need treatment for a condition that a specialist has decided it can help manage.

• FDA-approved indications: Sickle cell anemia with recurrent painful crises (adults, and children 2 years and older for certain products), resistant chronic myeloid leukemia, and certain squamous cell cancers of the head and neck (used with radiation).
• Other uses: Some specialists prescribe it for other blood disorders based on clinical judgment.

Whether it is right for a particular person depends on their diagnosis, blood counts, kidney and liver health, other treatments, and ability to attend regular monitoring.

Who Should Not Take Hydroxyurea

Tell your specialist before starting if any of the following apply.

• Allergy: You have had a serious allergic reaction to hydroxyurea or any ingredient in the product.
• Very low blood counts: Treatment may need to be delayed until blood counts recover.
• Pregnancy: Hydroxyurea can harm an unborn baby. It is not for use in pregnancy unless a specialist has determined that the benefit outweighs the risk.
• Kidney or liver disease: A lower dose or closer monitoring may be needed.
• Taking didanosine or stavudine: This combination should be avoided.
• Prior or planned radiation or chemotherapy: Blood counts may drop more.
• Active serious infection: Treatment may need to be delayed.
• Recent or planned live vaccines: Discuss timing with your specialist.

Your specialist will review the full list of precautions in the current FDA labeling for your product.

What to Do If You Miss a Dose

• Hydroxyurea is usually taken once daily. If you remember on the same day, take the dose as directed by your specialist or pharmacist.
• If you do not remember until the next day, skip the missed dose and go back to your regular schedule.
• Never take a double dose to make up for a missed one.
• If you are unsure what to do, or you miss more than one dose, contact your licensed medical specialist or pharmacist for guidance.
• Use a pill organizer, phone alarm, or dose log to help stay on schedule.

Related medications to Hydroxyurea

The right alternative depends on the condition being treated. Examples of options that may be used in similar situations include:

• For sickle cell anemia: L-glutamine, regular blood transfusions, stem cell (bone marrow) transplant, and gene therapies, depending on age and disease severity.
• For chronic myeloid leukemia: Tyrosine kinase inhibitors, such as imatinib, dasatinib, nilotinib, and others.
• For other blood disorders with too many blood cells: Options may include low-dose aspirin, phlebotomy, interferon, anagrelide, and ruxolitinib, depending on the condition.
• For head and neck cancers: Other chemotherapy and radiation combinations, and targeted or immune therapies, based on the tumor type.

These options differ in how they work, their side effects, and their monitoring needs. Do not switch or stop treatment on your own. Any change should be made only after talking with your licensed medical specialist.

Storage Instructions

• Temperature: Store capsules and tablets at room temperature, generally between 68°F and 77°F (20°C to 25°C), unless the label says otherwise.
• Moisture and light: Keep the medicine in the original tightly closed container, away from moisture (avoid bathrooms) and direct light and heat.
• Child safety: Keep all medicines locked or out of reach and sight of children and pets. Use child-resistant caps.
• Disposal: Do not throw away unused medicine in household trash unless instructed. Ask your pharmacist about safe disposal for hazardous drugs.

Disclaimer:

This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Patients must consult a licensed medical specialist, such as a hematologist or oncologist, depending on the condition being treated, before starting, changing, or stopping treatment. Treatment decisions must be based on a full clinical evaluation by a qualified specialist. If you think you are having a medical emergency, call your local emergency number right away.